A number of micro-machines utilize movable cantilevers, ribbon structures or other similar micro-structures. Typically, these-micro structures are extremely thin; on the order of hundreds or thousands of Angstroms, and are formed through release etch processes. These thin micro-structures can experience a high degree of stress and tension, either during fabrication and/or during operation of the device. Larger micro-structures can experience stress or tension on the order of 1.5 GPa or higher. Micro-support structures can fail under such conditions leading to device failure.
Optical MEM devices are used to modulate one or more wavelengths of light. Optical MEM devices can have applications in display, print and electrical device technologies. Examples of an optical MEM device which utilize suspended micro-ribbon structures to modulate light are disclosed in the U.S. Pat. Nos. 5,311,360, 5,841,579 and 5,808,797, all issued to Bloom et al., the contents of which are hereby incorporated by reference.
Briefly, an optical MEM device described in the above referenced patents has one or more sets of movable ribbons that comprise a support layer and a reflective top-layer. The support layer is preferably a silicon nitride layer and the reflective top-layer is preferably an aluminum layer. The ribbon structures are typically secured to a substrate through opposite ends of the ribbon, whereby center portions of the ribbons, referred to herein as the active portions, move up and down to modulate an incident light source.
For particular applications, most notable in optical communications, larger ribbon structures are preferred. As previously mentioned, these larger ribbon structures can be subject to high levels of stress and tension both in the fabrication of the device and during the operation of the device. Accordingly, there is a desire for MEM devices with mechanical support structures which are capable of supporting micro-structures exhibiting high stress and/or tension. Further, what is desirable is a method for controlling or tunning the resonant frequency or frequencies and/or the operating voltage or voltages required to deflect the active portions of ribbon structures in an optical MEM structure.